Mars-Pathfinder has been started now and human adaptation for microgravity due to long-term space flight becomes more important. Therefore, medical countermeasures for such adaptive change in space are most urgent, and indispensable. Artificial gravity is one of the most important target to be solved urgently and collaboratively. In the coming International Space Station (ISS) , an artificial gravity experirnental module is planned to be attached. But it is only for animal and not for human. We have emphasized in all occasions to set a human centrifuge in ISS in order to estimate the actual usefulness cf centrifugation effect on human as the prevention against cardiovascular deconditioning and bone mineral loss. Dr. Nicogossian and Dr. Vernikos are well recognized us, but they say this module is only for animal.On the other part, we have conducted the experiments using a short-arm human centrifuge to prevent the hematocrit increase caused by head down tilt bed rest for four days. This is a simulation study on the ground of proving the usefulness of centrifugation in space. 2G-1 hour Gz centrifugation was adopted every day during 4 days head down tilt for 10 healthy male subjects. We have succeeded to stop the increase of hematocrit up to 4 days of head down tilt, though Convertino et al. failed by other countermeasures using exercise or standing up on the bed for 1-2 hours, and water intake etc.More collaborative studies are necessary even internationally to solve the problem of artificial gravity; how much, how long and how often can we give them the centrifugation in space?